A continuous forging apparatus for forging a cast strand produced by continuous casting in its final solidification region during the process of drawing the cast strand from casting molds has been known, for example, as disclosed in Japanese Patent Application Laid-open No. 2-70,363. With such an apparatus, it is possible to mitigate center segregations and porous shrinkage cavities in cast strands, thereby advantageously improving the internal quality of products. However, the apparatus itself includes the following disadvantages and problems to be resolved.
(1) It is sometimes impossible to forge a cast strand with uniform forging reduction amounts on both sides by means of forging anvils because of warping of the cast strand to deviate from its transfer line. Such a warp of the cast strand is caused by uneven cooling in a secondary cooling zone for cooling the cast strand, wrong correction at junctions between strands of different steel kinds or at pinch roll arranged zones or the like. PA1 (2) The forging reduction force sometimes acts upon the apparatus as an external force rather than a working force for a cast strand. Therefore, the apparatus has a risk of being damaged to shorten its service life considerably.
(3) With an apparatus having hydraulic cylinders arranged for the purpose of preventing overload and adjusting the distance between anvils, in the case that the inner pressure in cylinders is different as high as 200 kg/cm.sup.2 depending on when forging is being effected or before the forging, volume of an hydraulic oil may change of the order of about 1% by compression. Even the anvils start to move away from each other from their positions nearest to each other, the reduction force remains corresponding to the compression of the hydraulic oil. Such a reduction force acts as a torque rotating the crankshaft in the reverse direction (simply referred to hereinafter "negative torque"). As there are clearances (backlashes) between tooth surfaces of gears in mesh with each other in a speed reduction device connected to the crankshaft, the torque rotating the crankshaft in the reverse direction causes the tooth surfaces of the gears to collide with each other so that strange sound (striking sound) and vibration occur which detrimentally affect the service life of the apparatus itself and make difficult the stable working of strands by the apparatus.
In order to solve the problems (1) and (2) as described above, the position control can be performed, for example, by the use of the hydraulic servo valve and the hydraulic control mechanism disclosed in Japanese Patent Application Laid-open No. 60-82,222. However, this system is expensive to increase the installation cost unavoidably. Moreover, hydraulic oil for controlling the apparatus must be kept in a highly clean state which requires a troublesome maintenance. Therefore, the system for hydraulically controlling the apparatus must be separated from general hydraulic systems. Such an arrangement is not suitable for practical use. There has been no means to overcome the problem (3).
It is an object of the invention to provide a forging apparatus for forging a cast strand produced by continuous casting during the process of drawing the cast strand from continuous casting molds, which is able to work the cast strand with uniform forging reduction amounts on both sides by causing anvils to follow the cast strand even if the cast strand is warped or floated and is also able to considerably mitigate strange sound and vibration of the installation occurring in the forging.